So you stumble upon a time travel machine. You can choose to travel into the past or the future, you can only go one way and once you get there you cant time travel again. Once you time travel you are STUCK in that time.

"Imagine that the train left the station on January 1, 2050. It circles Earth over and over again for 100 years before finally coming to a halt on New Year's Day, 2150. The passengers will have only lived one week because time is slowed down that much inside the train. When they got out they'd find a very different world from the one they'd left. In one week they'd have travelled 100 years into the future," Hawking writes.

Id go to the future. Reason: even if you could go to the past and fix your mistakes or do things different, you did those for a reason, to learn. You wouldnt be the person you are today if you didnt make those mistakes. Id like to take some stuff back that Ive done, but feel Im better for learning to not do that agian...just my .02